The spark ignition type internal combustion engine which adopts a fuel injection system instead of a conventional carburetor has come into wide use. In such an engine, fuel whose pressure has been raised by a fuel pump is injected into an intake manifold through an injector or injectors which is/are electrically turned ON and OFF. If the pressure of the fuel is kept at a predetermined pressure related to the internal pressure of the intake manifold, the quantity of fuel to be supplied to the engine can be precisely controlled by controlling the injection time.
According to, for example, Japanese Laid-open Patent Application No. 54-19021 (1979), a pressure booster which is driven by an engine shaft is employed in addition to a low-pressure fuel pump, whereby the necessary fuel pressure is secured. Further, at the starting of the engine, the fuel is injected for the first time after the fuel pressure has reached a predetermined value.
However, in an engine in which the necessary fuel pressure is attained by a fuel pump which is driven by a battery power supply, a starter motor is connected to the battery during the starting operation, so that the battery undergoes a high load and the fuel pump is not satisfactorily driven in some cases. Especially during cold conditions, the terminal voltage of the battery is decreased greatly when the battery is subjected to the high load and, hence, it is often the case that the fuel pressure required for the starting is not attained.